This invention relates to an improvement of an inner guide tube forming the curving end section, made of a flexible thin tube, of an endoscope, and more particularly to a structure by which the curving characteristic of the guide tube is improved and the collapse or abrupt bend thereof is prevented as much as possible when it is curved.
When the curving end section, made of a flexible thin tube, of an endoscope is inserted into a part of a human body to be examined, it is curved smoothly over a wide range of curve angles according to the conditions of a path to the aimed part of the human body or by an operating means for feeling for the part. For this curving operation, two angle wires connecting a manual operating section to the aforementioned end section are employed. However, if the curving pressure of the curving section is great, the tensions of the angle wires are increased in the curving operation. As a result, the durability of the wires is decreased. Furthermore, if a force for operating the angle wires is increased, it is rather difficult for the operator to feel the contact conditions of the end section with the manual operating section. Therefore, the operability of the endoscope is lowered.
Therefore, in the endoscope of this type, not only the outer pipe of the aforementioned flexible thin pipe but also the inner tube of the same should be so designed as to be readily curved. In order to meet this requirement, the wall thickness of the tube should be made thinner since in such a mechanism it is preferable to make the internal volume of the tube as large as possible and to make the outside diameter thereof as small as possible. If the wall thickness of the tube is merely reduced, however, the tube may be bent when it is curved, which will obstruct the further operation.
In order to overcome this difficulty, two methods have been proposed, in one of which a metallic coil whose diameter is such that the coil can be in close contact with the inner wall of a conventional tube is inserted thereinto, and in the other of which a metallic belt coiled to have a diameter which is substantially equal to the outside diameter of a tube is placed over the outer wall of the tube. However, the former method is not practical, because the internal volume of the tube is decreased, which will obstruct the insertion of forceps or the like, and in addition it becomes difficult to clean the inside of the tube because the inner wall of the tube becomes uneven because of the insertion of the coil, which results in the contamination or infection of bacteria or bacilli. On the other hand, the latter method is also disadvantageous because the tube's outside diameter is increased, and although the bend of the tube may be prevented, it is unsatisfactory in flexibility because the stiffness of the coil is added to that of the tube.
In order to overcome the disadvantage caused by the addition of the coil, there has been proposed a method in which a metallic belt is wound, in a coil state, around the outer wall of a tube and is then embedded in the tube by heat treatment. However, this method is still disadvantageous in that because the metallic belt is embedded in the tube, shrinkage occurs between the tube and the coil, and it is unexpectedly poor in flexibility.